Hi,
Just a small contribution (a light one)
Sorry for my english....
Many training and many exercices are made just with calculation and probability, without lots of true and established bases!
As for example a simple deco calc witch is always made from test,calculation and not usable for everybody(even if its real safe)!
In the army, close cicruit diving protocols are also based on test and guys who pass not threw long diving time in many conditions are not allowed to continue training and getting badge!!
But, from thousand and thousand of dives with CC , single or mixed gaz, there is a few accident because CO2 hits!
So I believe that we can continue to dive without additional control!
A man on the top of the Everest mountain knows his body and metabolism, don't need any gauge to balance o2 and co2!
You should you also know about your metabolism, and there is one solution for it!
Think about it (but a little less and) DIVE more often...........................
BEST REGARDS
Bernard